<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
      padding: 0;
    }

    .box {
      vertical-align: middle;
      display: inline-block;
      /* font-size: 50px; */
    }

    .box span {
      font-size: 30px;
      vertical-align: inherit;
    }

    .box span:first-child {
      font-size: 20px;
    }

    .box1 {
      vertical-align: middle;
      display: inline-block;
      font-size: 20px;
    }
  </style>
</head>

<body>
  <div class="box"><span>a</span><span>onef</span></div>
  <div class="box1">fff</div>
</body>

</html>